1. Field of the Invention
The present invention relates to a manufacturing method for a current collector single body sheet-like composite positive electrode which is a component in a polymer solid electrolyte cell and to a manufacturing method for a polymer solid electrolyte cell which uses said current collector single body sheet-like composite positive electrode.
2. Related Art
In general, a distinction is made between liquid electrolyte-type cells which use a liquid electrolyte and solid electrolyte-type cells which use a solid electrolyte.
Within the two classifications, there is a greater number of possible electrolyte substances for liquid electrolyte-type cells. This has led to greater advances in the development and use of such liquid electrolyte-type cells over solid electrolyte-type cells. However, when liquid electrolytes-type cells are used over a long period, there have been the problems of loss of electrolyte due to evapotranspiration and leaking of electrolyte which reduce the efficiency of the cell, with the latter problem having a further drawback in that leaking electrolyte can damage electronic equipment.
On the other hand, while the limited number of electrolyte substances has hindered the development of solid electrolyte-type cells, such cells do not suffer from the problems of decline in performance due to the loss of electrolyte through evapotranspiration or due to the leaking of the electrolyte (which can damage electronic equipment), in addition to having a further advantage of enabling reductions in both the size and weight of cells. As more portable electronic equipment, such as portable telephones and personal computers, has been developed, attention has been focussed on the use of these cells as a power source or as memory back-up cells, with lithium solid electrolyte-type secondary cells being noted in recent years for their high voltage and high energy density.
These lithium solid electrolyte-type secondary cells are generally constructed of a sheet-like negative electrode made of lithium metal, a sheet-like composite positive electrode made with a lithium compound as the active material in the positive electrode and a polymer solid electrolyte film positioned between the two electrodes as their power generation elements, with a positive and a negative current collector being formed on the outside of these elements. Out of these, it is the sheet-like composite positive electrode which is the power generation element with the greatest effect on the performance of the cell, so that in order to improve the performance of such electrodes, techniques for the combining of electrically conductive material, polymer solid electrolyte and non-aqueous solvent which are added to the active material in the positive electrode have already been developed. Here, techniques, such as the dispersion or dissolution of each material in a volatile solvent, the application of this solvent on electrodes and on flat plates by means of a screen coating method or a doctor blade method and then the removal of excess solvent by means of an evapotranspiration method, have been used as methods for forming sheets in the manufacturing process of these sheet-like composite positive electrodes.
However, for such conventional manufacturing methods, there has been coagulation of the dispersion materials, such as the active material and the conductive material, or of the dissolved material, such as the polymer solid electrolyte material, during solvent removal process. As a result, sheets produced by such methods suffer from an unequal dispersion of all of the materials, so that these sheet-like composite positive electrodes suffer from insufficient interaction between the materials, making it impossible to achieve the desired electrode performance.
As a further problem in conventionally manufactured electrodes, there has been insufficient electrical contact between the positive electrode and the current collector or between the polymer electrolyte film and the positive electrode, so that this too has prevented the realization of optimal performance of the electrodes.
Finally, since conventional manufacturing methods are methods for the applying of a volatile solvent into which the materials are dispersed or dissolved onto the flat plate, it becomes necessary to delicately adjust the viscosity of the solution, as well as to consider the prevention of any danger to workers when removing the solvent, meaning that such manufacturing methods are highly problematic.